Washington (state) — Referendum 71 — “This bill would expand the rights, responsibilities, and obligations accorded state-registered same-sex and senior domestic partners to be equivalent to those of married spouses, except that a domestic partnership is not a marriage. Should this bill be Approved or Rejected?”

The Positions: An Approve (Yes) vote upholds the expanded domestic partnership rights approved by the state legislature. A Reject (No) vote withdraws those rights and benefits, although it does not overturn domestic partnership itself.

The thing to notice is that the language is the functional opposite here of what it was in Maine or California. An affirmative (approve) vote is good news for same-sex couples, and a negative (reject) vote is bad for them. This has caused some confusion; one pollster has stated that as much as 10 percent of the electorate might vote in a way opposite to their true intentions.

The Polls: The only independent polling in the race is from SurveyUSA, which shows the Approve side winning 50-43, an improvement from 45-42 a month ago. GQR also polled the race on behalf of the pro-domestic partnership group Washington Families Standing Together and showed it passing 53-36, although the usual caveats apply as this is a nonindependent poll.

Analysis: Washington is similar to Maine in certain respects, being white and fairly secular, and since I think the pro-gay marriage side is more likely than not to prevail in Maine, you might think I feel the same way about the initiative in Washington state. Indeed I do feel that way, although the initiatives are not directly comparable. On the one hand, Referendum 71 does not go as far as Maine’s Question 1 or California’s Proposition 8 since it seeks to reaffirm an “everything but marriage” bill that does not formally bestow the title of marriage upon same-sex couples. On the other hand, a rejection of the referendum would not overturn Washington’s 2007 domestic partnership law, but instead only the expanded, marriage-like benefits that were afforded to those couples this year.

Were Washington to vote on a measure to ban domestic partnership outright, it would almost certainly fail and fail badly: by a 58-42 margin, according to my statistical model. A measure to ban gay marriage but not domestic partnership would be much closer; I have such a measure failing 52.5-47.5, but there is a good deal of uncertainty there, and in an off-year election the numbers might be closer to 50:50. Referendum 71 appears to be polling somewhere in between those two goalposts, which makes sense, since it takes Washington somewhere in between domestic partnership and full-blown marriage.

There is also arguably less uncertainty about the outcome in Washington than in Maine. This is because, as in California, most Washingtonians vote by mail, and SurveyUSA has the Approve side leading 53-42 among those who have already voted. A small bit of good fortune for the Approve side is that there is a highly competitive mayoral race in Seattle, which might encourage turnout in that obviously very liberal corner of the state.

The Odds: Although there is a lot of uncertainty in both the polling and the statistical model because of the ambiguity of the measure under consideration, they do tend to point toward the same result: Referendum 71 passing by a margin on the order of 7-10 points. Coupled with what appears to be movement toward the pro-domestic partnership side — which may reflect voters familiarizing themselves with the language of the ballot — and what also appears to be an advantage for the Approve side in votes collected thus far, Referendum 71 appears to be fairly safe. I would give about 10-1 odds against its being rejected.

Nate Silver is the founder and editor in chief of FiveThirtyEight. @natesilver538